1. Field of the Invention
The invention relates to a real-time compensation system and a real-time compensation method for use with a measuring apparatus.
Laser measuring apparatus are known per se, and typically include an interferometer which combines a reference beam, reflected from a stationary retroreflector, and a measuring beam reflected from a moving retroreflector, to generate interference which may be made manifest at a photodetector. Displacement of an object to which the moving retroreflector is connected may be measured by generating an incremental count from the output of the photodetector. In practice a plurality of photodetectors may be provided which, in conjunction with suitable signal processing electronics, generate a pair of digital quadrature pulses, thereby to generate information on both the magnitude and direction of movement of the object to which the movable retroreflector is connected. It is also known to provide one or more environmental sensors, which generate signals corresponding to values of, for example, ambient air temperature, air pressure, humidity, and so on. These signals may be used to correct measurements made with the laser.
2. Description of Related Art
EP 334541 discloses an error compensation system for a CNC machine tool in which positioning errors arise when a movable body is positioned by a servo. U.S. Pat. No. 5,375,066 discloses error correction to a machine tool in real time to correct fixed geometric errors, or thermally induced errors. This subject is also addressed in the following publications of the U.S. Department of Commerce National Institute of Standards and Technology NISTIR 4854, 4447 and 4832.